SPE vs DPE Ball Valve Seats
A single-piston-effect seat can move to relieve excess body-cavity pressure when the pressure relationship across the seat reaches the design condition. A double-piston-effect seat can seal from either side across the seat.
Combining SPE and DPE seats changes the isolation and cavity-pressure behavior of a trunnion ball valve, so abbreviations should not be selected without reviewing the required pressure cases.
State normal flow direction, isolation requirement, cavity-relief philosophy and relevant test cases in the inquiry so the seat arrangement is selected from the operating requirement rather than habit.